If current trends continue, missiles will replace gun systems completely in "first line" service.[citation needed] Guns are being increasingly pushed into specialist roles, such as the Dutch Goalkeeper CIWS, which uses the GAU-8 Avenger 30 mm seven-barrel Gatling gun for last ditch anti-missile and anti-aircraft defence. Even this formerly front-line weapon is currently being replaced by new missile systems, such as the RIM-116 Rolling Airframe Missile, which is smaller, faster, and allows for mid-flight course correction (guidance) to ensure a hit. To bridge the gap between guns and missiles, Russia in particular produces the Kashtan CIWS, which uses both guns and missiles for final defence. Two six-barrelled 30 mm Gsh-6-30 Gatling guns and 9M311 surface-to-air missiles provide for its defensive capabilities.
What is likely to entirely replace gun systems?
missiles

Initially Eisenhower planned on serving only one term, but as with other decisions, he maintained a position of maximum flexibility in case leading Republicans wanted him to run again. During his recovery from a heart attack late in 1955, he huddled with his closest advisors to evaluate the GOP's potential candidates; the group, in addition to his doctor, concluded a second term was well advised, and he announced in February 1956 he would run again. Eisenhower was publicly noncommittal about Nixon's repeating as the Vice President on his ticket; the question was an especially important one in light of his heart condition. He personally favored Robert B. Anderson, a Democrat, who rejected his offer; Eisenhower then resolved to leave the matter in the hands of the party. In 1956, Eisenhower faced Adlai Stevenson again and won by an even larger landslide, with 457 of 531 electoral votes and 57.6% of the popular vote. The level of campaigning was curtailed out of health considerations.
Who did Eisenhower want as his 1956 running mate?
Robert B. Anderson

Ion gauges are used in ultrahigh vacuum. They come in two types: hot cathode and cold cathode. In the hot cathode version an electrically heated filament produces an electron beam. The electrons travel through the gauge and ionize gas molecules around them. The resulting ions are collected at a negative electrode. The current depends on the number of ions, which depends on the pressure in the gauge. Hot cathode gauges are accurate from 10−3 torr to 10−10 torr. The principle behind cold cathode version is the same, except that electrons are produced in a discharge created by a high voltage electrical discharge. Cold cathode gauges are accurate from 10−2 torr to 10−9 torr. Ionization gauge calibration is very sensitive to construction geometry, chemical composition of gases being measured, corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low vacuum. The composition of gases at high vacuums will usually be unpredictable, so a mass spectrometer must be used in conjunction with the ionization gauge for accurate measurement.
What are the two types of Ion gauges?

hot cathode and cold cathode.